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Decontamination
This can be defined as removal of contaminants from the system by washing, heating, chemical treatment and mechanical cleaning. The term contaminant denotes the undesirable chemical entity present in the assets used for manufacture. The internal and external surfaces of equipment are exposed to chemicals during service. Thus the objectives of any decontamination process are
a) To reduce occupational exposure.
b) To salvage the facility, equipment and materials as far as possible.
c) To restore the site for future use which may be an alternate use (e.g. may be commercial rather than industrial).
The forms of contaminants are
a) Solids: Residues, products
b) Liquids: Residual liquids in reactors, tanks, heat exchangers, pumps
c) Vapors: Volatile chemicals in pipes, storage tanks
d) Aerosols: Liquid and solid particles suspended in air. This includes powders and dusts.
Decontaminate in Stages
A structured decontamination process is always carried out in multiple stages. Each stage results in the equipment progressively nearing the "clean" status.
These stages are:
a) Primary decontamination: This is the initial cleaning of equipment using chemicals and with water followed by steam/nitrogen/compressed air. The level of contamination is measured. If the contamination level is high, the next activity does not take place unless acceptable decontamination criterion is achieved.
b) Dismantling: The equipment is dismantled to check the presence of contaminant. The stage is also utilized to carry out inspection and testing of equipment to ascertain the utility of equipment for future use
c) Secondary decontamination: The dismantled parts of the equipment are cleaned with chemicals, water, steam and/or compressed air. The level of contaminant is measured at this stage. If the level of contaminant is high, the process is repeated again and again, till acceptable decontamination criterion is achieved.
d) Disposal of equipment: The equipment is declared fit for disposal. It can be sold off or put to use for other purpose (say transported to another location to set up the same plant again).
e) Disposal of waste: The process of decontamination generates liquid and solid waste. This is to be disposed off in a systematic manner. The liquid effluents go to the effluent treatment plant and the solid waste is sent for incineration or any other approved disposal method.
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Decontamination methods used to clean up the contaminants are
a) Standard: Water, Compressed Air
b) Non-standard: Steam, Caustic, Detergents, etc
The process of decontamination can take place naturally, if a chemically contaminated surface is exposed in air and allowed to be washed with water for a long period of time. The process has no control on time element and the decontamination results cannot be predicted on time line.
The second method uses chemical treatment, water treatment, steam treatment and the decontamination results can be predicted with reasonable accuracy.
The process flow diagram for the complete process is given below for better understanding.
